What does diphthong mean?
A diphthong is a single vowel sound that begins at one position in the mouth and glides toward another within the same syllable. English examples include the 'oy' in 'boy' and the 'ou' in 'loud': what a speaker hears as one vowel is actually a smooth movement between two qualities. The term comes from Greek roots meaning roughly 'double sound' and entered English in the early modern period through scholarly writing on language. Diphthongs are central to phonetics and phonology, where linguists classify them as rising, falling, opening, or closing depending on the direction and nature of the glide; different languages and even different regional accents use distinct sets of them. The word also has an older, orthographic sense referring to pairs of vowel letters written together for one sound. For students of languages, singers, actors, and poets, understanding diphthongs is practical: they shape accent, rhythm, and rhyme. Its natural counterpart, a steady unmoving vowel, is called a monophthong.
nounA diphthong is a complex vowel sound in which the tongue glides smoothly from one vowel position to another within a single syllable, as in the sounds of 'oy' in 'boy' or 'ou' in 'loud'. It can also refer to a digraph in spelling in which two vowels represent such a single sound.
- A phonetic unit: a single-syllable vowel sound produced by a glide from one vowel quality to another (e.g. the 'ow' in 'cow').
- In orthography and older usage: a digraph of two vowel letters representing a single sound (e.g. 'ai' in 'rain').
"The word 'coin' contains the diphthong /ɔɪ/, a single syllable that glides from one vowel quality to another."
"English learners often struggle to produce the diphthong in 'choice', flattening it into a pure vowel instead."
"The poet relied on long vowels and diphthongs to slow the pace of the closing lines."
The standard plural simply adds -s. It refers either to multiple such sounds within a language or across languages.
"Australian English is famous for the distinctive diphthongs in words like 'mate' and 'go'."
The word 'diphthong' itself contains two consonant clusters but no diphthong — its Greek roots literally mean 'double sound'.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of diphthong
Diphthong derives from the Ancient Greek 'diphthongos', formed from 'di-' ('twice') and 'phthongos' ('sound' or 'voice'), so the word literally means 'two sounds'. It passed into Latin as 'diphthongus' and entered English via scholarly Latin writing in the early modern period, with attestations from around the late sixteenth or early seventeenth century. The same Greek root appears in the linguistic terms monophthong and triphthong, coined later by analogy to describe one and three vocalic elements respectively.
How diphthong is actually used
Diphthong is a technical term used chiefly in linguistics, phonetics, language teaching, and discussions of poetry and pronunciation. It is neutral in register — formal in origin but familiar to anyone who has studied a foreign language or read about accents. The plural is straightforwardly 'diphthongs'. In everyday conversation it is rare, so using it signals some familiarity with language study rather than informality.
Easily confused with diphthong
A digraph is two letters written together representing one sound (like 'sh'), whereas a diphthong is specifically a gliding vowel sound — though some diphthongs are spelled with digraphs.
A monophthong is a pure, steady vowel sound held at one position, while a diphthong glides between two positions within one syllable.